In general, washing machines are appliances that wash laundry using water flow created by rotation of a washing tub or washing wings and impacts exerted by washing wings as well as emulsion actions by detergent. A washing machine proceeds with washing, rinsing, and/or dehydrating processes to get rid of dirt from objects to be washed (hereinafter, referred to as ‘laundry’) through an action between detergent and water.
A typical washing machine includes a casing forming an outer appearance thereof, an outer tub suspended in the casing, and an inner tub provided to be rotatable in the outer tub. Further, such washing machine includes a suspension to attenuate vibrations that occur to the outer tub when the inner tub and/or a pulsator rotate.
Typically, the suspension is configured to reduce vibrations occurring to the outer tub using elastic/restoring force of a spring and viscous force of a fluid. Such suspension may effectively reduce vibrations in a normal state where the outer tub vibrates within a constant amplitude range, but has a limitation in reducing vibrations in a transient state where the outer tub vibrates at a larger extent than that of the normal vibration state.
In other words, in case a typical suspension is designed to be optimized for the transient vibration state with a larger amplitude, the suspension exhibits a lower vibration attenuation effect in a normal vibration state with a relatively smaller amplitude. On the contrary, in case the suspension is designed to be optimized for the normal vibration state, the suspension may provide a sufficient vibration attenuation effect in the transient vibration state. Accordingly, there is a need for a method of effectively attenuating vibrations in both the normal vibration state and the transient vibration state.